Hint: it's not "the shoulder thing that goes up." https://www.youtube.com/watch?v=9rGpykAX1fo A barrel shroud is a piece that surrounds the barrel of a firearm. It's primary purpose is to provide a cooler surface which the person using the firearm can hold to stabilize the firearm. Not only does this feature have no impact on the lethality of the firearm, the definition in the legislation was written so poorly, it could have been construed to include handgun slides.